1. Field of the Invention
The present invention relates to a display device, and more particularly, to a transmission-type display device which uses a retardation film to enhance viewing angle.
2. Description of the Related Art
A liquid crystal display (“LCD”) device includes an LCD panel comprising a thin film transistor (“TFT”) substrate where TFTs are formed, a color filter substrate where color filters are formed, and a liquid crystal layer interposed between both substrates. The LCD panel does not emit light by itself, therefore a backlight unit is provided behind the TFT substrate to irradiate light. Further, polarizing plates adhere to external surfaces of both substrates, respectively, of which transmitting axes of the respective polarizing plates are perpendicular to each other.
The LCD device displays screen images by using an index of refraction anisotropy of the liquid crystal layer. Liquid crystal molecules of the liquid crystal layer rotate relative to an optic axis depending on an applied voltage. Accordingly, transmissivity of light through the liquid crystal layer may be adjusted by controlling a phase difference of light.
The liquid crystal molecules have birefringence that have an index of refraction of a major axis that is different from that of a minor axis. Due to the birefringence, an amount of light and a characteristic of color may vary depending on a position from which a user watches the LCD device, such as from the front or the lateral side. Accordingly, modification of contrast ratio, color shift, gray inversion, or the like may be generated in the LCD device using the liquid crystal molecules.
As display devices having a panel rotatable at 90 degrees for small-size mobile products have been developed, the viewing angle of the LCD device becomes more important. In a twisted nematic (“TN”) mode LCD device, the viewing angle from right and left sides is good while the gray inversion of the upper side and the lower side is problem. If the TN mode LCD device uses a wide view film, the viewing angle becomes wider while the gray inversion in the lower side and a diagonal direction is not easily removed.
A vertical alignment (“VA”) mode LCD device has been developed to improve the viewing angle and response time, which are problems in the TN mode LCD device. The VA mode LCD device includes an electrode patterned vertical alignment (“PVA”) or a pixel divided into multi-domain vertical alignment (“MVA”) to enhance the viewing angle. However, both the PVA and MVA involve a complex process of manufacture.